very simple, just hit enter!
$sql = "
select
this as that,
those as them
from
complextable1 as something,
complextable2 as otherthing,
..
Where
very complex condition
";
Nothing more to it; both PHP and mySQL will ignore the newline characters.
NOTE: I always use double quotes to enclose the string, that way I can use $variables and have them recognized.
Sam